Wireless communication system

ABSTRACT

A wireless communication system broadcasts a control signal at a first frequency band from a base station and allocates additional frequency band(s) for transmitting data via terminal(s). A control signal at the first frequency band indicates the location of the additional frequency band(s) and is not transmitted over the additional frequency band(s). Wireless data transmission is simultaneously performed over the first frequency band and the additional frequency band(s). Each terminal receives the control signal, which is used in time-synchronizing frames between the wireless data transmission at the first frequency band and the wireless data transmission at the additional frequency band(s). The control signal also includes control data for managing wireless data transmission between the base station and the terminal(s) at the first frequency band, and is utilized instead of a control signal at the additional frequency band(s).

This is a Continuation Application of co-pending application Ser. No.13/117,462 filed on May 27, 2011, which is a Divisional Application of(expired) co-pending application Ser. No. 10/432,994 filed on May 28,2003, which is a National Phase of PCT International Application No.PCT/JP01/10498 filed on Nov. 30, 2001. The entire contents of all of theabove applications are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a wireless communication systemcomprised of a base station and mobile stations, particularly to animprovement relating to inter-mobile station direct communication in awireless communication system based on a TDMA (Time Division MultipleAccess) system.

2. Background Art

A wireless communication system is comprised of a base station forgiving notices of allocations of bands (time regions for communications)and a plurality of mobile stations based on the TDMA system (in whichdifferent time regions are allocated to the mobile stations at the samefrequency for carrying out communication). For such a system, a PHSinter-mobile station direct communication system in accordance with RCRSTD-28 (second-generation cordless telephone system standard, version 1)of ARIB (Association of Radio Industries and Businesses) has beenproposed as a method of carrying out inter-mobile station directcommunication at a frequency other than that used by the base station.Improvements of the system are disclosed in JP Patent Publication(Kokai) Nos. 11-122663 A1(1999) and 11-341564 A1(1999), for example.

FIG. 13 shows an example of the frame structure in the TDMA wirelesscommunication system.

As shown in FIG. 13( a), a length of time in which the same frequency isused for communication is divided into frames 1 at predetermined timeintervals. In each frame (at predetermined periods), the base stationtransmits control information 2 to all of the mobile stations in awireless LAN area created by the base station. The control information 2includes information allowing the multiple mobile stations to besynchronized with the base station, and information indicating the band(time region) within the frame allocated to each mobile station.

The frame is divided into the time regions of DOWN-LINK 3 for thetransmission of data from the base station to the mobile stations andUP-LINK 4 for the transmission of data from the mobile stations to thebase station. In each time region, each mobile station is allocated aband 5 (band A) and a band 6 (band B), as shown in FIG. 13( b), suchthat the base station and the mobile stations can communicate with oneanother bi-directionally.

The control information 2 will be hereafter described by referring toFIG. 13( c).

Generally, in the physical layer of wireless systems, a digital signalcomprised of a preamble 200 for broadcast and a data payload 201 (datapayload 1, . . . , data payload N), which is information data fortransmission, is converted into an electric signal. The preamble 200located at the head identifies the signal received from a wirelessinterface. Particularly, the preamble 200 for broadcast that is attachedwhen the base station transmits broadcast information into a wirelesscell functions as a synchronization signal with which a mobile stationin the wireless cell attempts to achieve synchronization with the basestation. Further, the control information 2 includes such controlinformation as frame structure information and band allocationinformation.

FIG. 14 shows a block diagram of an example of the configuration of awireless LAN based on the above-described wireless communication system.

In FIG. 14, numeral 7 designates a WAN (Wide Area Network), and numeral8 designates a wireless LAN (Local Area Network). The wireless LAN 8 iscomprised of a plurality of mobile stations 11-13 and a base station 10.The base station 10 is either connected to a central control unit 9 forthe central control of band allocations, or is equipped with the centralcontrol unit 9 inside. The wireless LAN 8 is connected to the WAN 7 viathe base station 10.

The mobile stations 11 to 13 carry out a base station-mobile stationcommunication according to the band allocation information notified bythe base station 10. The communication paths are indicated ascommunication paths 14-16. The communication path for directcommunication between a mobile station 11 (mobile station <1>) and amobile station 12 (mobile station <2>) is indicated by a communicationpath 17.

When the mobile station 11 (mobile station <1>) transmits data to themobile station 12 (mobile station <2>), if the normal basestation-mobile station communication is employed, the same data wouldhave to be transmitted twice via the communication paths 14 and 15 shownin FIG. 14, which is inefficient. Thus, it is necessary to use a methodfor carrying out inter-mobile station direct communication by which datais directly transmitted between the mobile stations via thecommunication path 17 without the intervention of the base station 10.

FIG. 15 shows an example of the frame structure for inter-mobile stationdirect communication in a conventional wireless communication system.

In the example of FIG. 15, inter-mobile station direct communication isconducted at a frequency different from the one used by the base station10. One of the mobile stations that carry out inter-mobile stationdirect communication transmits control information 19 at the frequencyfor inter-mobile station direct communication. This frequency isdifferent from the frequency at which frame synchronization is achievedand communications are carried out according to the control information18 transmitted by the base station. The mobile stations that carry outthe inter-mobile station direct communication are provided with abase-station function for synchronizing their frames and allocatingbands.

Other examples of conventional techniques for carrying out inter-mobilestation direct communication include: a wireless LAN system and a PDC(Personal Digital Cellular) portable telephone employing the CSMA/CA(Carrier Sense Multiple Access with Collision Avoidance) systemaccording to the ISO/IEC (International Organization forStandardization/International Electrotechnical Commission) 8802-11 orthe IEEE (Institute of Electrical and Electronics Engineers) 802.11standards; HiperLAN according to the ETSI (European TelecommunicationsStandards Institute), which is a 3.5-generation system transitioninginto a 4^(th)-generation system to be standardized around the year 2010following PHS (Personal Handy-phone System) and the W-CDMA (WidebandCode Division Multiple Access); and the MMAC (Multimedia Mobile AccessCommunication System) wireless system according to the ARIB (Associationof Radio Industries and Businesses).

The IEEE802.11 and the HiperLAN will be briefly described below,although they do not have direct relevance to the present invention inthat the former is not a centrally controlled wireless system comprisinga central control unit for centrally controlling band allocations, andthat the latter is a system that employs the same frequency as that forbase station-mobile station communication.

FIG. 16 shows an example of communication according to the IEEE802.11system.

In FIG. 16, among mobile stations 1 to 4 in a wireless LAN area 20, whena mobile station <1> wishes to send information to a mobile station <2>,the mobile station <1> broadcasts an RTS (Request to Send) signal 21 and24. Each mobile station analyzes the RTS signal. When it is not aninformation transmission request directed to a particular mobilestation, the mobile station stands by. When the RTS signal is directedto a particular mobile station, the mobile station (mobile station <2>)transmits a CTS (Clear to Send) signal 22 and 25 to indicate that it isready to receive. In response, the mobile station <1> transmitsinformation via a MAC signal 23 and 26 to the mobile station <2>. Duringthese processes, the other mobile stations refrain from transmission fora certain time period to avoid collision of transmission signals.

FIG. 17 shows an example of the frame structure in the HiperLAN system.Parts or elements similar to those shown in FIG. 13 are designated bysimilar references.

In the HiperLAN system, a band 28 is provided in a TDMA frame 27 forcarrying out inter-mobile station direct communication. In this band 28,the base station ceases transmission to allow the mobile stations totransmit to each other, thus allowing base station-mobile stationcommunication and inter-mobile station direct communication to takeplace on a single frequency.

In a conventional wireless communication system, the frames forinter-mobile station direct communication and those for basestation-mobile station communication are not synchronized, as shown inFIG. 15. Thus, in order to obtain control information for synchronizingthe respective frames, the communication modes are switched. This is aprocess in which a mobile station terminates its connection with thebase station for base station-mobile station communication and then setsup a connection with the mobile station that has the base-stationfunction for carrying out inter-mobile station direct communication. Animproved method of obtaining broadcast information from the base stationis proposed by JP Patent Publication (Kokai) No. 11-122663 A1(1999), forexample, in which the switching is carried out intermittently.

However, the apparatus disclosed in the above publication has theproblem that the mobile station 11 (mobile station <1>) cannot carry outdata communication with the mobile station 12 (mobile station <2>) andthe base station 10 simultaneously, as shown in FIG. 14. In recentcommunication systems, there is an ongoing shift from voicecommunication by telephone to data communication. Thus, the aboveproblem means that, in the context of building a wireless LAN, themobile stations are intermittently cut off from the network, creatingfurther problems. For example, the base station may not be able totransmit data received from a connected WAN (such as the Internet) to adestination mobile station in the wireless LAN, or the base station maynot even recognize the presence of the mobile station due to the absenceof connection therewith.

The above discussion is based on the assumption of creating, forexample, a household wireless LAN (home network) comprised of a gatewayunit including a base station connected to the Internet outside, andmobile stations including household information appliances (such as arefrigerator, microwave oven, television, video server, or set-top box,for example). In this case, it would be problematic if the externalnetwork could not send video information to the video server when thevideo server is wirelessly transmitting video information to thetelevision, or if, when an air conditioner should be externallyoperated, the presence of the air conditioner on the network could notbe confirmed due to the termination of its connection to the basestation.

Further, in order to realize inter-mobile station direct communication,there is the additional problem of having to add the base-stationfunction to one of the mobile stations that is to act as the basestation.

It is an object of the invention to provide an efficient wirelesscommunication system that allows for base station-mobile stationcommunication even when inter-mobile station direct communication iscarried out at a frequency other than that of the base station, whichcan reduce the burden on the mobile stations by having the base stationcontrol inter-mobile station direct communication, and which allows aplurality of frequencies to be simultaneously used by a single basestation.

DISCLOSURE OF THE INVENTION

The invention provides a wireless communication system comprised of abase station and mobile stations wirelessly connected to the basestation, wherein the mobile stations can communicate with one anotherwithout the intervention of the base station, the system furthercomprising a synchronizing means, wherein

when a second frequency is used for an inter-mobile station directcommunication which is different from a first frequency used for a basestation-mobile station communication, the synchronizing meanssynchronizes a frame in the base station-mobile station communicationwith that in the inter-mobile station direct communication based oncontrol information used in the base station-mobile stationcommunication.

The invention provides a mobile station wirelessly connected to a basestation and capable of a base station-mobile station communication at afirst frequency and an inter-mobile station direct communication at asecond frequency that is different from the first frequency without theintervention of the base station, the mobile station comprising asynchronizing means for synchronizing a frame in a base station-mobilestation communication with that in an inter-mobile station directcommunication based on control information used in the basestation-mobile station communication.

The invention provides a base station in a wireless communication systemcomprised of the base station and mobile stations wirelessly connectedto the base station, the base station comprising an allocation means forallocating a second frequency for an inter-mobile station directcommunication which is different from a first frequency used for a basestation-mobile station communication in response to a request from amobile station.

The invention provides a base station in a wireless communication systemcomprised of the base station and mobile stations wirelessly connectedto the base station, the system capable of conducting a basestation-mobile station communication at a first frequency and aninter-mobile station direct communication at a second frequencydifferent from the first frequency without the intervention of the basestation, the base station comprising:

an allocation means for allocating bands in a frame for an inter-mobilestation direct communication based on a request from a mobile station.

The base station may comprise a carrying means for performing carriersensing at a plurality of available frequencies and for carryingavailable frequencies other than a frequency used by the base station.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows block diagrams of examples of a base station and a mobilestation in the wireless communication system according to the invention.

FIG. 2 shows an example of the frame structure in an inter-mobilestation direct communication in the wireless communication system.

FIG. 3 shows a block diagram of an example of a wireless LAN based onthe wireless communication system.

FIG. 4 shows a control sequence chart illustrating the flow of data inan example of communication in the wireless communication system.

FIG. 5 shows a flowchart of communication processes performed in thebase station in the wireless communication system.

FIG. 6 shows a flowchart of communication processes performed in themobile station in the wireless communication system.

FIG. 7 shows a control sequence chart illustrating the flow of data inthe wireless communication system according to the invention.

FIG. 8 shows a block diagram of band allocations in the wirelesscommunication system.

FIG. 9 shows a block diagram of frame allocations in the wirelesscommunication system.

FIG. 10 shows an example of a state of communication between the basestation and the mobile stations in the wireless communication system,and shows a block diagram of frame allocation in the wirelesscommunication system.

FIG. 12 shows an example of a state of communication between the basestation and the mobile stations in the wireless communication system.

FIG. 13 shows an example of the frame structure in a conventional TDMAwireless communication system.

FIG. 14 shows a block diagram of an example of a wireless LAN based onthe conventional wireless communication system.

FIG. 15 shows an example of the frame structure for an inter-mobilestation direct communication in the conventional wireless communicationsystem.

FIG. 16 shows an example of communication according to the IEEE802.11system.

FIG. 17 shows an example of the frame structure according to theHiperLAN system.

BEST MODE OF CARRYING OUT THE INVENTION

The invention will be hereafter described in detail by referring to theattached drawings.

First Embodiment

FIG. 1 shows a block diagram of a base station and a mobile station in awireless communication system according to the first embodiment of theinvention.

Referring to FIG. 1, numeral 30 designates a base station in thewireless communication system, and numeral 40 designates a mobilestation that communicates wirelessly with the base station 30. The basestation 30 includes a central control unit 31.

The base station 30 comprises a central control unit 31 for allocatingbands in a frame of a communication frequency in response to a bandallocation request; an antenna 32 for wireless transmission andreception; a wireless processing means 33 for detecting availablefrequencies; a frame processing means 34 for carrying out frameprocessing by which control information such as allocated bandallocation information is converted into transmission data; a wirelesscontrol means 35 for creating control information such as a framesynchronizing signal and band allocation information concerningallocations by the central control unit 31; and a line processing means36 for sending external transmission data to the frame processing means34 in a certain format in response to an instruction from the wirelesscontrol means 35. The central control unit 31 carries out calculationsfor time allocation, for example, and it may be either included in thebase station 30, as according to the present embodiment, or locatedoutside the base station 30.

The mobile station 40 comprises an antenna 42 for wireless transmissionand reception; a wireless processing means 43 for receivingcommunication data and sending it to the frame processing means 44; aframe processing means 44 for achieving frame synchronization based on acontrol signal received from the base station 30 and separating thecommunication data into control information and reception data; awireless control means 45 for decoding the band allocation informationand the like and preserving it as control information for use in thecommunication data transmission/reception processing; and a lineprocessing means 46 for sending external transmission data to the frameprocessing means 44 in a certain format in accordance with aninstruction from the wireless control means 45.

The wireless control processing means 45 notifies the wirelessprocessing means 43 of the start of a transmission/reception operationupon encountering an allocated band (time) in a frame. In the case ofinter-mobile station direct communication, the wireless controlprocessing means 45 notifies the wireless processing means 43 of achange of frequency to that used for inter-mobile station directcommunication.

In accordance with the present embodiment, the wireless communicationsystem comprises a synchronizing means for synchronizing, when a secondfrequency is to be used for inter-mobile station direct communicationthat is different from a first frequency used for base station-mobilestation communication, frames between the base station-mobile stationcommunication and the inter-mobile station direct communication, on thebasis of control information used in the base station-mobile stationcommunication. The wireless communication system also comprises anallocation means for allocating bands and a frequency for inter-mobilestation direct communication in accordance with an allocation requestfrom the base station 30 or mobile station 40. The base station 30 andmobile station 40 each comprise a transmission means and a receptionmeans for transmitting and receiving allocation requests and allocationnotifying information between them. The mobile station 40 furthercomprises a control means for changing the wireless frequency inaccordance with an allocation. Thus, a base station-mobile stationcommunication can be carried out simultaneously with an inter-mobilestation direct communication. The base station 30 also carries outcarrier sensing at a plurality of available frequencies and comprises ameans for carrying available frequencies other than that used by thebase station 30.

FIG. 2 shows an example of frame structure in inter-mobile stationdirect communication according to the present wireless communicationsystem, showing examples of frame structure and band allocation. Theframe structures correspond to those of the conventional example shownin FIG. 15.

Referring to FIGS. 2( a) and (b), the frame structure is divided intotime regions consisting of control information 50, a communication bandDOWN-LINK 51, and a communication band UP-LINK 52. The controlinformation 50 includes information for a plurality of mobile stations40 to achieve synchronization with a base station 30 in each frame (atpredetermined periods), and information indicating a band (time region)in a frame allocated to each mobile station. The DOWN-LINK 51 is forsending data from the base station 30 to the mobile stations 40. TheUP-LINK 52 is for sending data from the mobile stations 40 to the basestation 30. The control information 50 includes a preamble 200 forbroadcast and a data payload 201, as described with reference to FIG.13( c). The preamble 200 for broadcast includes a synchronizing signalfor the mobile stations in a wireless cell to achieve synchronizationwith the base station, and control information such as frame structureinformation and band allocation information.

Referring to FIG. 2( b), a mobile station carries out inter-mobilestation direct communication at an inter-mobile station directcommunication frequency which is different from the frequency at whichframe synchronization is achieved and communication is carried out basedon the control information 50 transmitted by the base station 30. Themobile station synchronizes frames between base station-mobile stationcommunication and inter-mobile station direct communication by utilizingthe base station-mobile station communication control information 50instead of the control information 53 for the conventional inter-mobilestation direct communication. Numeral 54 designates a directcommunication band.

FIG. 2( c) shows an example of band allocation in base station-mobilestation communication. Numeral 55 designates control information wherethe control information 50 is allocated. Numeral 56 designates a band D1where the DOWN-LINK 51 is allocated. Numeral 57 designates a band U1where the UP-LINK 52 is allocated.

FIG. 2( d) shows an example of band allocation in inter-mobile stationdirect communication. As described above, the control information(control information 53) for the conventional inter-mobile stationdirect communication is not used, because the base station-mobilestation communication control information 50 is also used for theinter-mobile station direct communication. Numeral 58 designates a bandDi1 where the direct communication band 54 is allocated.

Thus, by synchronizing frames between base station-mobile stationcommunication and inter-mobile station direct communication, it becomespossible to process in parallel the communication band DOWN-LINK 51 fromthe base station 30 to the mobile stations 40, the communication bandUP-LINK 52 from the mobile stations 40 to the base station 30, and thedirect communication band 54 from one mobile station 40 to anothermobile station 40.

Hereafter, the operation of the wireless communication system asconfigured above will be described.

FIG. 3 shows a block diagram of an example of a wireless LAN based onthe present wireless communication system. Parts or elements similar tothose shown in FIG. 14 are designated by similar references.

In FIG. 3, a wireless LAN 8 is comprised of a plurality of mobilestations 40A to 40C, and a base station 30 with a central control unit31 built inside. The wireless LAN 8 is connected to a WAN 7 via the basestation 40.

The mobile stations 40A to 40C are similar in structure to those mobilestations 40 shown in FIG. 1, and they carry out base station-mobilestation communication in accordance with band allocation informationnotified from the base station 40. The communication paths are indicatedby communication paths 14 to 16. A communication path for inter-mobilestation direct communication between the mobile station 40A (mobilestation <1>) and the mobile station 40B (mobile station <2>) isindicated by a communication path 17.

An example of band allocation for the base station 30 and the mobilestation 40A (mobile station <1>) that wants to communicate with themobile station 40B (mobile station <2>) will be described by referringto FIG. 2.

In FIGS. 2 and 3, the mobile station 40A (mobile station <1>) receivesframe synchronization and band allocation based on the controlinformation 55 from the base station 30. A band 56 (band D1) is acommunication band from the base station 30 to the mobile station 40A(mobile station <1>). A band 57 (band U1) is a communication band fromthe mobile station 40A (mobile station <1>) to the base station 30. Aband 58 (band Di1) is a communication band from the mobile station 40A(mobile station <1>) to the mobile station 40B (mobile station <2>). Bycarrying out communication according to these allocations, the mobilestation 40A (mobile station <1)) can perform data communicationsimultaneously with the mobile station 40B (mobile station <2>) and thebase station 30 without interrupting its connection with the basestation 30.

FIG. 4 shows a control sequence chart indicating the flow of data in theabove example of communication. The numbers in the drawing show theindividual processing steps.

In FIG. 4, it is assumed that the mobile station 40A (mobile station<1>) and the mobile station 40B (mobile station <2>) have completedconnection with the base station 30 and have started communicationtherewith (60).

Initially, the mobile station 40A (mobile station <1>) transmits arequest (61) and another request (62) to the base station 30 in anallocated band of the UP-LINK 52. The request (61) calls for theallocation of a band for inter-mobile station direct communication fortransmitting data to the mobile station 40B (mobile station <2>). Therequest (62) calls for the allocation of a band for normal basestation-mobile station communication.

The mobile station 40B (mobile station <2>) also transmits a request(63) to the base station 30 in an allocated band of the UP-LINK 52,calling for the allocation of a band for normal base station-mobilestation communication.

The base station 30 then transmits an allocation request (64) to thecentral control unit 31 which bundles the band allocation requestinformation from each mobile station and the band allocation requestfrom the base station 30 to the mobile station.

The central control unit 31, in response to the band allocation request(64), notifies the base station 30 of information about the allocationsof bands in the next frame of the base station-mobile stationcommunication frequency and the inter-mobile station directcommunication frequency (65).

The base station 30 transmits, in the control information band in thenext frame, information about the band and frequency allocation fordirect communication from the mobile station 40A (mobile station <1>) tothe mobile station 40B (mobile station <2>) (66), and basestation-mobile station communication band allocation information (67,68) to the mobile station 40A (mobile station <1>) and the mobilestation 40B (mobile station <2)). Each mobile station carries outreception processing on the control information band.

The base station 30, in an allocated band in the DOWN-LINK 51 at thebase station-mobile station communication frequency, transmits basestation-mobile station communication data (69, 70) to the mobile station40A (mobile station <1>) and the mobile station 40B (mobile station<2>). Each mobile station carries out reception processing on anallocated band.

The mobile station 40A (mobile station <1>) transmits inter-mobilestation direct communication data (71) to the mobile station 40B (mobilestation <2>) in an allocated band for direct communication of theinter-mobile station direct communication frequency. The mobile station40B (mobile station <2>) carries out a reception processing on anallocated band.

The mobile station 40A (mobile station <1>) and the mobile station 40B(mobile station <2>) transmit base station-mobile station communicationdata (72, 73) to the base station 30 on an allocated band in the UP-LINK52. The base station 30 carries out a reception processing on anallocated band.

FIG. 5 shows a flowchart of the communication processing in the basestation 30. S indicates the steps thereof

Initially, in a carrier sensing process in step S11, availablefrequencies are detected by the wireless processing means 33 (FIG. 1) ofthe base station 30. Of the frequencies that are detected, one that isused by the base station 30 is selected, and preparations are made fortransmission and reception. At the same time, notification offrequencies available for inter-mobile station direct communication isgiven to the central control unit 31. Simultaneously, notification ofavailable frequencies other than those used by the base station 30 isgiven to the central control unit 31.

In the process of transmitting a control signal in step S I2, thewireless control means 35 creates control information including a signalfor frame synchronization and band allocation information allocated bythe central control unit 31. The control information is converted intotransmission data by the frame processing means 34, and then transmittedvia the wireless processing means 33 and antenna 32.

In the process of transmitting the communication data in step S13, theline processing means 36 transmits external transmission data to theframe processing means 34 in accordance with instructions from thewireless control means 35. The data is converted into transmission databy the frame processing means 34 and then transmitted via the wirelessprocessing means 33 and antenna 32.

In the process of receiving the communication data in step S14, thewireless signal is received by the antenna 32 and the wirelessprocessing means 33. The received data is separated into controlinformation and reception data by the frame processing means 34. Thecontrol information such as a band allocation request is processed bythe wireless control means 35, and necessary information is transmittedto the central control unit 31, where it is processed. The receptiondata is transmitted to the outside by the line processing means 36 afterbeing set in an external format.

In step S15, it is determined whether or not communication is finished.If not, the process resumes from step S11 and the above-described stepsare repeated. If the communication is finished, the present processcomes to an end.

FIG. 6 shows a flowchart of the communication processing performed inthe mobile station.

In a carrier sensing step of step S21, available frequencies aredetected by the wireless processing means 43.

In the process of receiving the control signal in step S22, framesynchronization is carried out based on the control signal transmittedfrom the base station 30 and received by the antenna 42 and the wirelessprocessing means 43. The control signal is converted into controlinformation by the frame processing means 44. The wireless controlprocessing means 45 decodes band allocation information and the likefrom the control information and stores it as control information foruse during the process of transmitting and receiving communication data.

Upon reaching an allocated band (time) in a frame, the wireless controlprocessing means 45 notifies the wireless processing means 43 of thestart of a transmission/reception operation.

In step S23, it is determined whether or not the communication isinter-mobile station direct communication. If so, the wirelessprocessing means 43 is notified of a change of frequency to that usedfor inter-mobile station direct communication in step S24. Thetransmission/reception frequency is then changed and the routineprogresses to step S25. If the communication is not inter-mobile stationdirect communication, the routine progresses to step S25.

In the process of transmitting and receiving communication data in stepS25, the wireless processing means 43 receives the communication dataand sends it to the frame processing means 34, where the data isseparated into control information and reception data. The controlinformation is processed by the wireless control means 35. The receptiondata is sent to the outside by the line processing means 36 after beingset in an external format. External transmission data is sent by theline processing means 36 to the frame processing means 34 in accordancewith an instruction from the wireless control means 35, where the datais converted into transmission data and then transmitted by the wirelessprocessing means 43 and antenna 42.

In step S26, it is determined whether or not there is a band. If thereis a band, the routine returns to step S23 to repeat the above-describedprocesses. If not, it is determined in step S27 whether or notcommunication is finished. If not, the routine returns to step S21 torepeat the relevant steps. If the communication is finished, the presentprocess comes to an end.

Thus, in accordance with the present embodiment, the wirelesscommunication system comprises a synchronization means for, when thecentral control unit 31 uses a second frequency for inter-mobile stationdirect communication which is different from the first frequency usedfor base station-mobile that communication, synchronizing frames betweenbase station-mobile station communication and inter-mobile stationdirect communication based on the control information used in basestation-mobile station communication. The system also comprises anallocation means for allocating a band and frequency for theinter-mobile station direct communication in accordance with anallocation request from the base station 30 or the mobile stations 40.Because the control information 55 for base station-mobile stationcommunication is utilized instead of the control information for thenormal inter-mobile station direct communication in synchronizing framesbetween base station-mobile station communication and inter-mobilestation direct communication, it is possible to process in parallel theband DOWN-LINK 51 for communication from the base station 30 to themobile stations 40, the band UP-LINK 52 for communication from themobile stations 40 to the base station 30, and the band 54 forcommunication from one mobile station 40 to another mobile station 40.

Thus, an inter-mobile station direct communication and a basestation-mobile station communication can be simultaneously conducted, orthe inter-mobile station direct communication can be conducted whilemaintaining connection with the base station 30, even when theinter-mobile station direct communication is conducted at a frequencyother than that of the base station 30.

Further, because the base station controls the inter-mobile stationdirect communication, the burden on the mobile stations can be reduced.

Second Embodiment

In the second embodiment, the manner in which communication bands areallocated is changed.

FIG. 7 shows a control sequence illustrating the flow of data in thewireless communication system according to the second embodiment of theinvention. FIG. 8 shows a block diagram of band allocation in thepresent wireless communication system, which corresponds to FIG. 2.

A wireless LAN can be constructed by using the present wirelesscommunication system in the same manner as described in FIG. 3.

Referring to FIG. 7, it is assumed that the base station 30, mobilestation 40A (mobile station <1>), mobile station 40B (mobile station<2>), and mobile station 40C (mobile station <3>) all have theircommunication lines open (80).

The mobile station 40C (mobile station <3>) transmits a communicationband request (81) to the base station. The mobile station 40A (mobilestation <1>) transmits a communication band request (82) to the mobilestation 40B (mobile station <2>).

In response to these band requests, the central control unit 31allocates a band 92 (band D1) and a band 93 (band U1) as communicationbands between the base station 30 and the mobile station 40C (mobilestation <3>) (83). The central control unit 31 also allocates a band 94(band D2) and a band 95 (band U2) as communication bands between themobile station 40A (mobile station <1>) and the mobile station 40B(mobile station <2>) (84). Numeral 91 designates control information.According to these allocations, the base station 30 and the mobilestation 40C (mobile station <3>) communicate with each other (85, 87),while the mobile station 40A (mobile station <1>) and the mobile station40B (mobile station <2>) communicate with each other (86, 88).

In accordance with the wireless communication system of the presentembodiment, the base station 30 instructs that the inter-mobile stationdirect communication between the mobile station 40A (mobile station <1>)and the mobile station 40B (mobile station <2>) be conducted at afrequency other than that of the base station 30. Thus, the base station30 can communicate with the mobile station 40C (mobile station <3>).

When the direct communication between the mobile station 40A (mobilestation <1>) and the mobile station 40B (mobile station <2>) isconducted at the same frequency as that of the base station 30, the basestation 30 cannot transmit or receive data on that band. However, inaccordance with the present embodiment, the base station 30 can transmitand receive data on all of the bands (times) in the frame because thedirect communication between the mobile stations 40A and 40B isconducted at a different frequency.

Thus, an efficient wireless communication system can be realized inwhich a single base station can use a plurality of frequencies forcommunication.

Third Embodiment

This is an example where the manner in which communication frame bandsare allocated is changed.

FIG. 9 shows a block diagram of frame allocation in the wirelesscommunication system according to the third embodiment of the invention,indicating examples of band allocations in frames for the basestation-mobile station communication frequency and the inter-mobilestation direct communication frequency.

A wireless LAN can be constructed using the present wirelesscommunication system in the same manner as described in FIG. 3.

Referring to FIGS. 3 and 9, the base station 30 broadcasts framesynchronization and band allocations in control information 100.Down-link phases D1 (101), D2 (102), D3 (104), and D4 (103) areallocated bands for transmission from the base station 30 to the mobilestation 40A (mobile station <1>), mobile station 40B (mobile station<2>), mobile station 40C (mobile station <3>), and mobile station 40D(mobile station <4>) (not shown in FIG. 3), respectively. Similarly,Up-link phases U1 (107), U2 (108), U3 (106), and U4 (105) are allocatedbands for transmission from the mobile station 40A (mobile station <1>),mobile station 40B (mobile station <2>), mobile station 40C (mobilestation <3>), and mobile station 40D (mobile station <4>), respectively,to the base station 30. A1 (109) is an allocation band for a directcommunication between the mobile station 40A (mobile station <1>) andthe mobile station 40B (mobile station <2>). While in this example thenumber of the direct communication frequency is one, there may be morethan one such frequency as long as they can be used in the wirelesscommunication system.

FIG. 10 shows an example of communication between the base station andthe mobile stations in the present wireless communication system,illustrating the state of communication at each communication terminalallocated in FIG. 9.

The base station 30 broadcasts the control information (including bandallocation information) for frame synchronization, transmits informationto the individual mobile stations in D1, D2, D3, and D4, and receivesinformation from the individual mobile stations in U1, U2, U3, and U4.In this example, the states of communication in about four frames areillustrated on the assumption that there is no change in allocations.

The mobile station 40A (mobile station <1>) receives the controlinformation from the base station 30, receives information from the basestation 30 in D1, and transmits information to the base station 30 inU1. The mobile station 40A (mobile station <1>) carries out a directcommunication with the mobile station 40B (mobile station <2>) in anallocation A1 at a frequency different from that for the basestation-mobile station communication, as shown in the second and thirdframes from the head.

Thus, the mobile station 40A (mobile station <1>) can directlycommunicate with the mobile station 40B (mobile station <2>) while atthe same time communicating with the base station 30. Further, becausethe direct communication is carried out at a separate frequency, thebase station 30 can communicate with the mobile station 40C (mobilestation <3>) and mobile station 40D (mobile station <4>), even while thedirect communication is taking place.

Fourth Embodiment

This is an example where the manner in which bands in a communicationframe are allocated is changed.

FIG. 11 shows a block diagram of frame allocation in the wirelesscommunication system according to the fourth embodiment of theinvention, illustrating examples of band allocations in frames for basestation-mobile station communication and inter-mobile station directcommunication frequencies.

A wireless LAN can be constructed by using the present wirelesscommunication system in the same manner as described in FIG. 3.

Referring to FIGS. 3 and 11, for the base station-mobile stationcommunication frequency, control information (110) for framesynchronization, Down-link phases D1 (111), D2 (112), D3 (114), and D4(113) are allocated bands for transmission from the base station to themobile station 40A (mobile station <1>), mobile station 40B (mobilestation <2>), mobile station 40C (mobile station <3>), and mobilestation 40D (mobile station <4>) (not shown in FIG. 3), respectively.Up-link phases U1 (117), U2 (118), U3 (116), and U4 (115) are allocatedbands for transmission from the mobile station 40A (mobile station <1>),mobile station 40B (mobile station <2>), mobile station 40C (mobilestation <3>), and mobile station 40D (mobile station <4>), respectively,to the base station. A1 (121), A2 (120), A3 (123), A4 (119), and A5(122) are allocations for direct communication between the mobilestations <2>and <3>, the mobile stations <1>and <3>, the mobile stations<1>and <2>, the mobile stations <1> and <4>, and the mobile stations <3>and <4>.

FIG. 12 shows an example of communication between the base station andthe mobile stations in the present wireless communication system,illustrating the state of communication at each communication terminalallocated in FIG. 11.

For example, in D1 where the mobile station 40A (mobile station <1>) iscommunicating with the base station, the mobile station 40A (mobilestation <1>) cannot communicate with any other mobile station unless themobile station 40A (mobile station <1>) is provided with a plurality ofwireless transmission/reception units.

Thus, the central control unit 31 (FIG. 3) provides allocations fordirect communication in bands other than D1, as shown in FIG. 12.

In the present embodiment, the central control unit 31 calculatescombinations for carrying out base station-mobile station communicationand inter-mobile station direct communication based on the bandallocation requests from each mobile station and the base station,provides efficient allocations that maximally utilize the wirelessbands, as shown in FIG. 11, and notifies the base station 30 as well asbroadcasts to each mobile station about their allocations. By such acentralized manner of control, frequencies can be completely utilizedwithout the stand-by times for avoiding collision of signals that arerequired in autonomous decentralized systems such as according toIEEE802.11. Furthermore, the central management of the requests forinter-mobile station direct communication and base station-mobilestation communication by the single central control unit 31 allowstransmission and reception to occur without collision of allocations.

In the above-described embodiments, the invention is applied to awireless communication system comprising the base station 30, the mobilestations 40 wirelessly connected to the base station 30, and the centralcontrol unit 31 provided within the base station 30 for allocating bandsin the frames of communication frequencies in response to bandallocation requests. However, the invention can be applied to any systemas long as it is a TDMA-based wireless communication system. Forexample, the invention can be applied to cordless telephone systems inwhich a master unit is connected to a plurality of slave units viawireless communication, PDAs (Personal Digital Assistants) with wirelesscommunication capabilities, and small-sized notebook personal computers.

The wireless communication system may also be comprised of a pluralityof identical wireless terminals having functions both as base stations,namely masters that manage communications, and as mobile stations,namely slaves that follow the master's instructions, each wirelessterminal carrying out both base station and mobile station operations.

INDUSTRIAL FIELD OF APPLICABILITY

Thus, the wireless communication system according to the inventionallows inter-mobile station direct communication and base station-mobilestation communication to take place simultaneously, or inter-mobilestation direct communication to take place while maintaining connectionwith the base station, when inter-mobile station direct communication iscarried out at a frequency other than that of the base station (seeFIGS. 9 and 10).

Further, because the base station controls inter-mobile station directcommunication, the burden on the mobile stations can be reduced.

Further, because inter-mobile station direct communication can becarried out at a second frequency that is different from the firstfrequency used in base station-mobile station communication, the basestation can carry out transmission or reception of data even in timeregions where inter-mobile station direct communication is taking place,for example. Thus, an efficient wireless communication system can berealized in which the base station can utilize a plurality offrequencies for communication.

1. A method of using a wireless communication system having a basestation and one or more terminals, the wireless communication systemcarrying out wireless data communication by use of a first frequencyband, the method comprising: employing a centralized CSMA/CA and/orTDMA/TDD system as a wireless access system; periodically broadcastingfrom the base station a control signal at the first frequency band, thecontrol signal configured to manage wireless data transmission of theone or more terminals; allocating, via the base station, in addition tothe first frequency band, one or more frequency bands different from thefirst frequency band for data transmission by the one or more terminals,wherein the control signal at the first frequency band indicates thelocation of the one or more frequency bands which can be used, thecontrol signal not being transmitted at the one or more frequency bands;simultaneously performing the wireless data transmission at the firstfrequency band and the wireless data transmission at the one or morefrequency bands; receiving, at each of the one or more terminals, thecontrol signal, which realizes a time synchronization of the wirelesscommunication system, and thus, based on the time synchronizationbetween the base station and the one or more terminals, the wirelessdata transmission at the one or more frequency bands istime-synchronized with the wireless data transmission at the firstfrequency band; wherein, the control signal at the first frequency bandcomprises control data configured to manage wireless data transmissionbetween the base station and the one or more terminals at the firstfrequency band, the control signal at the first frequency band beingutilized instead of a control signal at the one or more frequency bandsthat is configured to manage wireless data transmission between the oneor more terminals at the one or more frequency bands, the control signalat the first frequency band being utilized in synchronization of framesbetween the wireless data transmission at the first frequency band andthe wireless data transmission at the one or more frequency bands,permitting the simultaneous wireless data transmission both on the firstfrequency band and on the one or more frequency bands.
 2. The methodaccording to claim 1, further comprising: carrying out, at the basestation, carrier sensing at a plurality of frequency bands available asthe one or more frequency bands; determining, at the base station, theone or more frequency bands to be used; and notifying the one or moreterminals of information indicating the allocation of the one or morefrequency bands by use of the control signal transmitted from the basestation.
 3. The method according to claim 1, further comprising:periodically receiving at each of the one or more terminals, in accordwith the time synchronization at each terminal, the control signaltransmitted from the base station; wherein the wireless datatransmission of the terminal is time-synchronized on the first frequencyband and the one or more frequency bands; and the wireless datatransmission of the terminal at the first frequency band and thewireless data transmission of the terminal at the one or more frequencybands can be simultaneously carried out.
 4. A method of using a basestation of a wireless communication system having the base station andone or more terminals, the wireless communication system carrying outwireless data communication by use of a first frequency band, the methodcomprising: employing a centralized CSMA/CA and/or TDMA/TDD system as awireless access system; periodically broadcasting a control signal atthe first frequency band, the control signal configured to managewireless data transmission of the one or more terminals; allocating, viathe base station, in addition to the first frequency band, one or morefrequency bands different from the first frequency band for datatransmission by the one or more terminals, wherein the control signal atthe first frequency band indicates the location of the one or morefrequency bands which can be used, the control signal not beingtransmitted at the one or more frequency bands; simultaneously receivingfrom the one or more terminals the wireless data transmission at thefirst frequency band and the wireless data transmission at the one ormore frequency bands; wherein a time synchronization of the wirelesscommunication system is realized by the control signal transmitted fromthe base station at the first frequency band to each of the one or moreterminals, and thus, based on the time synchronization between the basestation and the one or more terminals, the wireless data transmission atthe one or more frequency bands is time-synchronized with the wirelessdata transmission at the first frequency band; and the control signal atthe first frequency band comprises control data configured to managewireless data transmission between the base station and the one or moreterminals at the first frequency band, the control signal at the firstfrequency band being utilized instead of a control signal at the one ormore frequency bands that is configured to manage wireless datatransmission between the one or more terminals at the one or morefrequency bands, the control signal at the first frequency band beingutilized in synchronization of frames between the wireless datatransmission at the first frequency band and the wireless datatransmission at the one or more frequency bands, permitting thesimultaneous wireless data transmission both on the first frequency bandand on the one or more frequency bands.
 5. The method of using a basestation according to claim 4, further comprising: carrying out carriersensing at a plurality of frequency bands available as the one or morefrequency bands, determining the one or more frequency bands to be used;and notifying the one or more terminals of information indicating thelocation of the one or more frequency bands by use of the controlsignal.
 6. A method of using a terminal station of a wirelesscommunication system comprised of a base station and at least theterminal, the wireless communication system carrying out wireless datacommunication by use of a first frequency band, the method comprising:employing a centralized CSMA/CA and/or TDMA/TDD system as a wirelessaccess system; receiving a periodically-broadcast control signal fromthe base station at the first frequency band, the control signalconfigured to manage wireless data transmission by the terminal; andsimultaneously carrying out the wireless data transmission at the firstfrequency band and wireless data transmission at one or more frequencybands different from the first frequency band, the one or more frequencybands allocated by the base station in addition to the first frequencyband for the wireless data transmission by the terminal station, thecontrol signal of the first frequency band indicating the location ofthe one or more frequency bands which can be used, the control signalnot transmitted at the one or more other frequency bands, wherein a timesynchronization of the wireless communication system is realized by thecontrol signal received by the terminal station, and thus, based on thetime synchronization between the base station and the terminal, thewireless data transmission at the one or more frequency bands istime-synchronized with the wireless data transmission at the firstfrequency band; and the control signal at the first frequency bandcomprises control data configured to manage wireless data transmissionbetween the base station and the terminal at the first frequency band,the control signal at the first frequency band being utilized instead ofa control signal at the one or more frequency bands that is configuredto manage wireless data transmission between the one or more terminalsat the one or more frequency bands, the control signal at the firstfrequency band being utilized in synchronization of frames between thewireless data transmission at the first frequency band and the wirelessdata transmission at the one or more frequency bands, permitting thesimultaneous wireless data transmission both on the first frequency bandand on the one or more frequency bands.
 7. The terminal stationaccording to claim 6, wherein: the wireless data transmission by theterminal station is time-synchronized on both the first frequency bandand the one or more frequency bands; and the wireless data transmissionof the terminal at the first frequency band and the wireless datatransmission at the one or more frequency bands can be simultaneouslycarried out.
 8. A method of using a wireless communication system havinga base station, a first terminal, and a second terminal, the wirelesscommunication system carrying out base station-terminal wireless datacommunication and inter-terminal direct wireless data communication byuse of a first frequency band, the method comprising: carrying out, inthe first terminal and the second terminal, the inter-terminal directwireless data communication in a state of being connected to the basestation; employing a centralized CSMA/CA and/or TDMA/TDD system as awireless access system; periodically broadcasting, from the basestation, a control signal at the first frequency band, the controlsignal configured to manage wireless data transmission of at least thefirst and second terminals; allocating, via the base station, inaddition to the first frequency band, one or more frequency bandsdifferent from the first frequency band for data transmission by atleast the first and second terminals, wherein the control signal at thefirst frequency band indicates the location of the one or more frequencybands which can be used, the control signal not being transmitted at theone or more frequency bands; simultaneously performing the wireless datatransmission at the first frequency band and the wireless datatransmission at the one or more frequency bands; receiving, at least atthe first and second terminals, the control signal, which realizes atime synchronization of the wireless communication system, and thus,based on the time synchronization between the base station and at leastthe first and second terminals, the wireless data transmission at theone or more frequency bands is time-synchronized with the wireless datatransmission at the first frequency band; transmitting, from the firstterminal to the base station a request signal, for setting upinter-terminal direct wireless data communication between the firstterminal and the second terminal; and transmitting, from the basestation to the first terminal, a response signal of the request signal,wherein the control signal at the first frequency band comprises controldata configured to manage wireless data transmission between the basestation and at least the first and second terminals at the firstfrequency band, the control signal at the first frequency band beingutilized instead of a control signal at the one or more frequency bandsthat is configured to manage wireless data transmission between at leastthe first and second terminals at the one or more frequency bands, thecontrol signal at the first frequency band being utilized insynchronization of frames between the wireless data transmission at thefirst frequency band and the wireless data transmission at the one ormore frequency bands, permitting the simultaneous wireless datatransmission both on the first frequency band and on the one or morefrequency bands.
 9. A method of using a base station in a wirelesscommunication system having the base station, a first terminal, and asecond terminal, the wireless communication system carrying out basestation-terminal wireless data communication and inter-terminal directwireless data communication by use of a first frequency band, the methodcomprising: employing a centralized CSMA/CA and/or TDMA/TDD system as awireless access system; periodically broadcasting a control signal atthe first frequency band, the control signal configured to managewireless data transmission of at least the first and second terminals;allocating, in addition to the first frequency band, one or morefrequency bands different from the first frequency band for the datatransmission by at least the first and second terminals, wherein thecontrol signal at the first frequency band indicates the location of theone or more frequency bands which can be used, the control signal notbeing transmitted at the one or more frequency bands; receiving from thefirst terminal, a request signal for setting up inter-terminal directwireless data communication between the first terminal and the secondterminal; and transmitting to the first terminal a response signalresponsive to the request signal, wherein a time synchronization of thewireless communication system is realized by the control signaltransmitted from the base station at the first frequency band andreceived by each of at least the first and second terminals, and thus,based on the time synchronization between the base station and at leastthe first and second terminals, the wireless data transmission at theone or more frequency bands is time-synchronized with the wireless datatransmission at the first frequency band; the control signal at thefirst frequency band comprises control data is configured to managewireless data transmission between the base station and at least thefirst and second terminals at the first frequency band, the controlsignal at the first frequency band being utilized instead of a controlsignal at the one or more frequency bands that is configured to managewireless data transmission between at least the first and secondterminals at the one or more frequency bands, the control signal at thefirst frequency band being utilized in synchronization of frames betweenthe wireless data transmission at the first frequency band and thewireless data transmission at the one or more frequency bands,permitting the simultaneous wireless data transmission both on the firstfrequency band and on the one or more frequency bands, the firstterminal and the second terminal carry out the inter-terminal directwireless data communication in a state of being connected to the basestation, and the wireless data transmission at the first frequency bandand the wireless data transmission at the one or more frequency bandscan be simultaneously carried out.
 10. A method of using a firstterminal station of a wireless communication system having a basestation, the first terminal, and a second terminal, the wirelesscommunication system carrying out base station-terminal wireless datacommunication and inter-terminal direct wireless data communication byuse of a first frequency band, the method comprising: carrying out theinter-terminal direct wireless data communication with the secondterminal in a state of both terminals being connected to the basestation; employing a centralized CSMA/CA and/or TDMA/TDD system as awireless access system; periodically receiving from the base station abroadcast including a control signal at the first frequency band, thecontrol signal configured to manage wireless data transmission of atleast the first and second terminal stations; simultaneously performingthe wireless data transmission at the first frequency band and thewireless data transmission at one or more frequency bands allocated bythe base station in addition to the first frequency band, the one ormore frequency bands being different from the first frequency band forthe data transmission of the first terminal, the control signal at thefirst frequency band indicating the location of the one or morefrequency bands which can be used, the control signal not being includedat the one or more frequency bands; transmitting to the base station arequest signal, for setting up inter-terminal direct wireless datacommunication between the first terminal and the second terminal; andreceiving from the base station a response signal responsive to therequest signal, wherein a time synchronization of the wirelesscommunication system is realized by the control signal transmitted fromthe base station at the first frequency band and received by the firstterminal, and thus, based on the time synchronization between the basestation and the first terminal, the wireless data transmission at theone or more frequency bands is time-synchronized with the wireless datatransmission at the first frequency band; the control signal at thefirst frequency band comprises control data configured to managewireless data transmission between the base station and the firstterminal at the first frequency band, the control signal at the firstfrequency band being utilized instead of a control signal at the one ormore frequency bands that is configured to manage wireless datatransmission between the one or more terminals at the one or morefrequency bands, the control signal at the first frequency band beingutilized in synchronization of frames between the wireless datatransmission at the first frequency band and the wireless datatransmission at the one or more frequency bands, permitting thesimultaneous wireless data transmission both on the first frequency bandand on the one or more frequency bands.